1. Field of the Invention
This invention relates to paperboard lids having a radiation cured overprint varnish. Such structures of this type, generally, protect the graphics which are printed upon the paperboard lid such that the graphics are not distorted and/or marred.
2. Description of the Related Art
Platen sealing is gaining popularity for attaching paperboard lids to trays following product filling. The benefits of this method include more uniform seals, simpler equipment operation, and the ability to seal through food contamination. A major disadvantage with this method is that the heated platen can blemish the outside surface of the lid which contains important sales graphics and, in some cases, UPC symbols. The blemished or marred surface results in an unsatisfactory package appearance and, in some cases, UPC symbols which cannot be scanned.
It is known, in coating systems, to make use of a varnish layer to protect a printed surface. Exemplary of such prior art is U.S. Pat. No. 4,170,681 ('681) to J. R. Edwards et al., entitled "Method of Applying a Varnish Layer to a Printed Surface and Product Made Thereby". While the '681 reference teaches the use of a varnish layer to provide a smooth protective surface for the printed graphics, the nature of the varnish layer is such that it is not heat resistant (mass stable) to temperatures above 325.degree. F. and also the varnish is not radiation cured. Consequently, an advantageous overprint varnish would be one which is both heat resistant and radiation cured.
It is apparent from the above that there exists a need in the art for an overprint varnish which is capable of protecting the graphics printed upon the lid, but which at the same time is heat resistant and radiation cured. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.